Conventionally techniques employed to detect whether an internal combustion engine knocks or not are known. Japanese Patent Laying-open No. 2001-227400 discloses a knock control device for an internal combustion engine that can accurately determine whether the engine knocks. The knock control device described in Japanese Patent Laying-open No. 2001-227400 includes a signal detection unit detecting a vibration waveform signal generated in the internal combustion engine, a generation period detection unit detecting as a generation period a period for which the vibration waveform signal detected by the signal detection unit has at least a predetermined value, a peak position detection unit detecting a peak position in the generation period detected by the generation period detection unit, a knock determination unit determining from a relationship between the generation period and the peak position whether the internal combustion engine knocks, and a knock control unit controlling the internal combustion engine's operation state in accordance with a decision made by the knock determination unit. The knock determination unit determines that the engine knocks when the peak position relative to the generation period falls within a predetermined range. The signal detection unit detects a predetermined frequency component unique to a knock signal as the vibration waveform signal.
In the knock control device for an internal combustion engine, as described in this publication, a vibration waveform signal generated in the internal combustion engine is detected by a signal detection unit and a generation period, for which the vibration waveform signal has at least a predetermined value and its peak position are detected by a generation period detection unit and a peak position detection unit, respectively. It is thus found at which position in the generation period of the vibration waveform signal a peak is attained, and therefrom, whether the internal combustion engine knocks is determined by the knock determination unit and in accordance with such decision the internal combustion engine's operation state is controlled. When the peak position relative to the generation period falls within a predetermined range, i.e., if a waveform has a form having a peak position appearing earlier in the generation period of the vibration waveform signal that has a predetermined length, it is recognized as a waveform provided uniquely when the engine knocks. Whether the internal combustion engine knocks can thus also accurately be determined when the internal combustion engine's operation state rapidly changes, such as in transition, in turning on/off an electrical load, and the like. The internal combustion engine's operation state can thus be controlled appropriately.
The knock control device for an internal combustion engine as described in Japanese Patent Laying-open No. 2001-227400 allows a frequency component unique to knocking to be detected as a vibration waveform signal. However, such adaptation that allows the frequency component unique to knocking to be detected removes a noise component corresponding to a vibration component that is not attributed to knocking and as a result the noise component's characteristic portion (e.g., the timing of the occurrence of the vibration, the vibration's damping rate, and the like) is removed. As a result, if a vibration is attributed to noise, a waveform analogous to that of a vibration attributed to knocking can be obtained. In that case, it is difficult to distinguish the vibration attributed to knocking and that attributed to noise and whether the engine knocks cannot determined with precision. The knock control device for an internal combustion engine as described in Japanese Patent Laying-open No, 2001-227400, however, fails to provide any consideration to such issue.